When evaluating whether a given earth formation contains valuable materials, such as fluid hydrocarbons, a core sample of the earth formation may be procured. For example, a coring tool, which may include a coring bit configured to remove earth material around a columnar core sample, may be placed at the bottom of a borehole and rotated under load to form a core sample. As the coring tool advances, the core sample may be received into an inner barrel within the coring tool, which may be configured to contain the core sample during retrieval and reduce (e.g., minimize) contamination until the core sample can be analyzed. When the core sample is returned to the surface, the core sample, any fluids entrapped within the core sample, and any fluids that escaped the core sample but were captured by the coring tool may be analyzed to determine the characteristics exhibited by the earth formation.
To ensure that the core sample more accurately represents the actual characteristics of an earth formation at the end of a borehole, steps are taken to reduce the likelihood that contaminants enter the inner barrel that is to receive the core sample. For example, an entrance to the inner barrel may be sealed shut while advancing the coring tool into the borehole to reduce the likelihood that materials other than the core sample (e.g., drilling fluid and particles suspended within the drilling fluid) enter the inner barrel and contaminate the core sample. The entrance to the inner barrel may be sealed shut by, for example, an activation module that is intended to block the entrance to the inner barrel while the coring tool is advanced into the borehole and to unblock the entrance to the inner barrel when a core sample is introduced into the inner barrel. As a further example, the inner barrel may be substantially emptied of material and then filled, and potentially pressurized, with a presaturation fluid (i.e., a fluid of known composition that will not contaminate the core sample) before the coring tool is introduced into the borehole. The presaturation fluid may be selected such that a sponge material lining the interior of the inner barrel is not wettable by the presaturation fluid. The sponge material, however, may be a material that is wettable by a fluid of interest expected to be found within the core sample, such as oil or other hydrocarbons.